Most integrated circuit packages share a substantially standard construction. Specifically, the actual circuitry is on a semiconductor die, which is mounted, usually by adhesive, to a relatively large (as compared to the die) mass or “slug” which acts as a heat sink.
The die has a plurality of bond pads through which power, ground, and signals are communicated outside the die. Bond wires are bonded, typically by a process known as “wirebonding,” to the bond pads. The other ends of the bond wires are wirebonded to one of a plurality of metallic lead fingers, or package leads, that lay on the heat sinking mass but are separated from it by a non-conductive layer. The non-conductive layer is typically an insulating adhesive tape, although it may be other materials such as a ceramic layer bonded to the heat sinking mass.
The package leads are generally formed by stamping from a single sheet of suitable conductive metal. The portions which are to protrude from the package as pins are joined together by a rectangular band of metal at their outer extremities, forming a unit known as a leadframe. To assemble the integrated circuit package, the insulating layer is applied to the heat sinking mass, and the leadframe is attached in place. The die is subsequently affixed, and the wire leads are wirebonded to the appropriate bond pads and package leads.
The entire assembly is then encased in a plastic or epoxy “mold compound” with ends of the package leads protruding as pins for connection to external devices.
As integrated circuit devices become more complex, the die sizes are becoming smaller. Decreasing die sizes have resulted in finer bond pad pitches, longer bond wire lengths, and closer wire-to-wire separation. At the same time, bond wire diameters are becoming thinner.
With the increase of bond wire span, reduction of bond wire diameter, and reduction in wire-to-wire separation, various problems arise in the assembling of packages for these integrated circuits. One particularly glaring problem is that, during molding, liquefied molding materials flow over the top of the die, causing adjacent bond wires to come into contact with each other to form short-circuits.
Accordingly, it would be highly desirable to provide an improved integrated circuit package that overcomes the problems associated with increasing bond wire span, reduced bond wire diameter, and reduced wire-to-wire separation.